This invention relates to fluid meters and, more particularly, to a fluid meter of the internal gate rotary vane type.
Rotary vane fluid meters with an internal sealing gate are generally well known. Such meters require a timing mechanism between the rotor and the gate to avoid collision, to set the desired rotational velocity of the gate relative to the rotor, and to propel the gate from the rotor. The most commonly used type of timing mechanism is gearing. An example of such a meter using gearing is disclosed in U.S. Pat. No. 3,482,446, which issued on Dec. 9, 1969, to Wrinkle et al. While gear systems such as that disclosed in the Wrinkle et al patent have the advantage of allowing a different rotational velocity between the gate and the rotor in a simple form, such systems also suffer from a number of disadvantages. Gear systems have significant rubbing action, creating friction, which is detrimental to a fluid meter's performance because friction effects accuracy in a variable manner. Such gear systems must also allow some clearance, or backlash, to minimize the friction. This has a detrimental effect in fluid meters due to gear noise. This gear noise can be meshing noise (generally a problem because spur gears are used to reduce friction) or backlash induced noise (because of pressure pulsations from internal and/or external sources). Gear systems also require either self-lubrication (such as plastic) which severely limits gear velocity, or a lubricating oil bath which effects meter accuracy due to oil drag. The most significant problem with gear systems is breakage, which results in catastrophic failure. Accordingly, it is a primary object of this invention to eliminate gearing timing systems in internal gate rotary vane fluid meters.
A major impediment to nqn-geared systems is that most mechanisms that might be candidates have significant velocity limitations due to either imbalance or oscillation characteristics. Thus, for example, the cam drive disclosed in U.S. Pat. No. 226,829, which issued on Apr. 27, 1880, to Bergquest, requires the gate to accellerate/decellerate very rapidly when the rotor vane passes through the gate pocket, thus severely limiting rotational velocity (which limits the meter's capacity) due to torsional vibration and strength of material. Accordingly, it is another object of this invention to provide a direct drive between the rotor and gate which does not have any oscillation or torsional vibration which would limit rotational velocity and thus limit capacity.
Another major impediment to non-geared systems is that the rotational velocity of components within the direct drive mechanisms can be far higher than that of the rotor/gate system which, because of bearing friction, can result in poor accuracy due to friction loads as well as limited capacity due to limiting system rotational velocity for bearing life. For example, the system disclosed in U.S. Pat. No. 3,448,615, which issued on June 10, 1969, to Schneider, Jr., provides various means for the rotor to drive the gate through wheels or rollers which run on cam shaped surfaces on the rotor vanes. Such a device does, or can, have constant velocity of the rotating elements, including the wheels or rollers, but requires the wheels or rollers to operate at a very high rotational velocity, compared to the rotor or gate, thus adding significant bearing friction load as well as limiting capacity in the desire to lower roller or wheel velocity. Accordingly, it is a further object of this invention to provide a direct drive which limits the number of bearings to reduce the friction load which effects meter accuracy. Still another object of this invention is to provide a direct drive which minimizes the rotational velocity of the component bearings to minimize both the friction load and the bearing wear or endurance.
A further impediment to non-geared systems is that direct drive mechanisms can severely limit the capacity per revolution of the meter, requiring either very low capacity in order to keep the rotational velocity down, or very high velocity for acceptable capacity, which results in friction and reduced bearing life. For example, the meter disclosed in U.S. Pat. No. 1,994,397, which issued on Mar. 12, 1935, to Loveridge et al, provides a multiple crank drive consisting of crank discs in the gate. Such a method of direct drive severely limits the meter's capacity or requires very high rotational velocity to achieve acceptable capacity, due to the discs severely limiting the gate pocket size. Such increased velocity results in high bearing friction and reduced bearing life. Accordingly, it is still a further object of this invention to provide a meter drive system having maximum capacity per revolution of the meter to minimize the necessary rotational velocity of all components for reduced bearing friction and longer bearing life.
Yet another object of this invention is to provide a direct gearless drive mechanism for an internal gate rotary vane fluid meter which results in constant rotational velocity of all components, a constant value of torque and inherent balance.